Parallel manipulators with three translational degrees of freedom (3T DOF) and one rotational degree of freedom (1R DOF) have a wide range of applications such as assembly, pick-and-place and machine loading, as well as haptic devices. A few 3T1 R parallel manipulators have been proposed so far.
3T1R parallel manipulators are proposed by R. Clavel (in U.S. Pat. No. 4,976,582 issued on Dec. 11, 1990), Luc H. Rolland (in “The Manta and the Kanuk: Novel 4-DOF Parallel Mechanisms for Industrial Handling,” proceedings of 1999 International Mechanical Engineering Congress and Exposition), and F. Pierrot et al. (in “H4 Parallel Robot: Modeling, Design and Preliminary Experiments,” proceedings of 2001 IEEE Conference on Robotics and Automation). The 3T1R parallel manipulators described in these references present such disadvantages as having four legs of different architecture or as having spherical joints.
A 4-DOF parallel manipulator is proposed by Z. Huang (in “Kinematics of a Special 3-DOF, 3-TPT Parallel Manipulator,” proceedings of ASME 2002 Design Engineering Technical Conference and Computers and Information in Engineering Conference, DETC2002/MECH-34322). The 4-DOF parallel manipulator described has three legs, each formed of a prismatic joint (hereinafter “P-joint”) between a pair of universal joints (hereinafter “U-joint”), hence referred to as a 3-UPU 3R1T parallel manipulator.
Recently, a systematic study on the type synthesis of parallel manipulators has been presented by T. L. Yang et al. (in “Structure Synthesis of 4-DOF (3-Translation and 1-Rotation) Parallel Robot Mechanisms Based on the Units of Single-Opened Chain,” proceedings of ASME 2001 Design Engineering Technical Conference and Computers and Information in Engineering Conference, DETC2001/DAC-21152). Three types of four-legged 3T1R parallel manipulators with legs of the same type and no inactive P-joint are proposed. However, only two of the proposed architectures are functional, while the other one in which the four translational DOF of the cylindrical joints (hereinafter “C-joints”) are actuated is flawed. In the latter case, the four translational degrees of freedom of the C-joints cannot control the translational degree of freedom of the moving portion along the direction perpendicular to all the axes of the four C-joints. Moreover, the manipulators disclosed by Yang et al. are limited to specific conditions that restrict the possible configurations of the manipulators.
Keeping in mind that it is desired to have parallel manipulators having topologically similar legs and no passive P-joints, broader conditions could be set to incorporate a wider range of 3T1R parallel manipulators. By having general conditions describing groups of configurations limiting output motion of parallel manipulators to three translational DOF and one rotational DOF, 3T1R parallel manipulators could be better adapted for given requirements.